Csound is a computer programming language for dealing with sound. It is called Csound because it is written in the C programming language, as opposed to some of its predecessors. Csound was written at Massachusetts Institute of Technology by Barry Vercoe, based on an earlier language called MUSIC-N. It is free software, available under the LGPL.

In a simple usage, the programmer supplies Csound with two specially formatted or real-time audio stream as output.

It has been developed over many years and currently has a vast amount of opcodes (modules). One of it s greates strengths is that it is completely modular and expandable by the user.

The orchestra and score files may be unified into a single structured file using XML tags. Here is a very simple example of a unified Csound data file which produces a wave file containing a one second sine wave tone of 1 Kilohertz at a Sampling frequency of 44.1 kHz:

; csound -W -d -o tone.wav sr = 44100 ; Sample rate. kr = 4410 ; Control signal rate. ksmps = 10 ; Samples pr. control signal. nchnls = 1 ; Number of output channels.

instr 1 a1 oscil p4, p5, 1 ; Simple oscillator. out a1 ; Output. endin

f1 0 8192 10 1 ; Table containing a sine wave. i1 0 1 20000 1000 ; Play one second of one kHz tone. e

As with many other programming languages, writing long programs in Csound can be eased by using an integrated environment for editing, previewing, testing, and Debugging. Such environments are available.

Csound is the underlying language for the Structured Audio extensions to MPEG-4.

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